Piston



Jan. 3, 1939. F. JARDINE 7 PISTON Filed Jan. 21, 1955 S ShQ t S-Sheet l Snventor 5 M m m;

(Ittornegd Jan. 3, 1939 JARDINE 1 2,142,272

PISTON Filed Jan. 21, 1955 s Sheets-Sheet s Zinnentor PEA NA .TAIED/MF Br I Qflornegs remation-3, 1939 UNITED STATES, PATENT-OFFICE fauaz'izj r PISTON Frank Jardine, Cleveland, Ohio, assignor to Aluriinum Company of America, Pittsburgh, 2a.,

a corporation of Pennsylvania Application January 21, 1935, Serial No. 'aeso' "s Claims. ((21. 309-11 invention relates tointe'rnal combustion engine pistons composed of light metal, such as aluminum alloy, in combination with,-or designed for operation in, engine cylinders composed of 5 metal having a lower co eflicient ofthermal' expansion than the metal ,of the pistons, and spe-.

ciflcally to the type of piston in which the excess expansion of the skirt is absorbed by-flexing the skirt, so that a close flt may :be maintaind be- 10 tween the skirt and cylinder wall in operation.

The. object of this inventionds to so distribute the flexing necessary to absorb the excessexpansion of the piston skirt as to reduce to a minimum the amount of flexing to which 'any'particular portion, of the skirt is subjected and at the same-time to distribute the bearing pressure of the skirt upon the cylinder wall so as to attain uniform unit bearing pressures from the top to the bottom of the skirt and fro nthe center of each'thrust or bearing face to the edge of the portion of the face bearing at any particular time on the cylinder wall, so asto reduce ,to a minimum the unit bearing pressure to which any portion of the skirt is subjected at anytime during operation of the piston. v

This object is'attained by making the piston with ahead havinga depending ring flange of the usual type, wrist pin bosses integrally and rigidly connected with the head and a substantially full round skirt integral'with the wrist pinbosses but separated at its upper edge from the head on each side by arcuate horizontal slots. The skirt is further provided on one side with a substantially vertical slot extending from about the center-of one of the horizontal slots downwardlyvtoward but terminating short of the open end of the skirt, leaving a circumferentiaily continuous band at the bottom of the skirt below the wrist pin bosses. The skirt is finished to a generally oval contour with the longer axis perpendicular to the wrist pin axis.

The results oi maintaining a uniform distribution of both the bearing pressures andthe flexin; are minimized wear, high fatigue resistance, and complete freedom from seizing orscoring eveniwhen the pistons are fitted to the cylinder walls at clearances as small as .0005 of an inch per inch of diameter and operated at speeds as high as 4500 to 5000 R. ,P. M. 7

Referring to the drawin which illustratev a preferred embodimentof this invention:-

Figure 1 is,a'vertical sectional view through a piston constructed in accordance with this invenv I v oval contour disclosed and claimed in my prior 55 tion;

I Figure 2 is a view partly in elevation and'partly in vertical section through the wrist pin axis; Figure 3 is a view partly in elevation and partly in section looking at the open end of the pis- I ton; 5 Figure4 is a side elevation of the piston; Figure 5 is a diagram illustrating in exaggerated form the cross sectional relation of the piston and ac'ast iron cylinder when cold;

Figure '6 is a diagram illustrating in exaggerat- 10 ed form the cross sectional relation of the oylinder and piston when heated up to a point ap-- proaching full operating temperature; and

Figure '7 is a vertical sectional view through the cylinder and piston illustrating the relation ll of the connecting rod and crank during the power stroke.

Referring to the drawings the piston illustrated therein embodies a head i0 having a depending cylindrical flange ii grooved on the outside for $0 the reception of piston rings and aligned wrist pin bosses i2 integral with and depending below the ring flange. The wrist pin bosses are preferably rigidly braced from the head as by ribs l3. The skirt indicated generally at it is relatively thin 25 walled and is integral with the outer ends of the wrist pin bosses.

The two sides of the skirt i5 and it between the wrist pin bosses are termed thrust or hearing faces; I5 being the minimum thrust-face de- I signed and arranged in the engine to receive the lateral thrust of the piston on the compression stroke, and i6 being the maximum thrust face arranged to receive the lateral thrustoi. the power stroke.

In the finished piston'the upper edges of the thrust faces i5 and it are separated from the ring flange by oppositely disposed arcuate horizontal Theskirt is finished to an oval contour with its major axis perpendicular to the wrist pin axis.

Desirably the contour of the skirt may be symmetrically oval, or elliptical, or the differential Patent No. 1,939,778, issued December 19, 1933 may be The piston is combined with an engine cylinder Cwhich has substantially less thermal expansion than the piston itself. Preferably the cylinder is composed of cast iron in order to obtain the best bearing surface for the piston, and also to reduce to a minimum the friction and wear. Cast iron has a substantially smaller coefllcient. of thermal expansion than the light metal alloy of which the pistons are composed, and in addition the cylinder is ordinarily cooled by a circulating fluid to dissipate the heat of combustion, so that the temperature of the cylinder is less than the temperature of the piston during normal operation.

The piston is secured to a connecting rod 29 by a wrist pin 20, the latter preferably being journailed both in the bosses l2 and the end of the connecting rod. The opposite end of the connecting rod 29 is Journalled to a crank pinil, forming a part of a crankshaft 32.

The inner bearing wall of the cylinder 0 is ground truly cylindrical. The relationship between the piston skirt and the cylinder wall when the parts are cold is illustrated in exaggerated formin Figure 5. -The relationship when the parts have been partially heated to their operating temperature is illustrated in Figure 6. In Figure 5 the line AA represents the wrist pin axis and the minor axis of the piston skirt, and the line 3-3 represents the major axis of the skirt.

The piston is preferably fitted to the cylinder when cold with a clearance of about .0005 of an inch per inch of diameter at the ends of the major axis BB, or in other words for a 3" pistona clearance of about .0015. The diameter A-A of the skirt I4 is preferably about .006of an inch shorter than the diameter BB. From each end of the diameter BB moving about the piston skirt to the ends of the diameter A-A the clearance of the piston from the cylinder wall increases gradually, the increase being insufllcient, however, to permit lateral slapping or rattling of the piston by movement of the piston along the wrist pin axis.

The wall of the piston is preferably relieved slightly about the outer ends of the wrist pin bosses as by cast reliefs 25, or in any other suitable manner. When the cast reliefs are used, in order to maintain the necessary metal section. the interior surface of the wall of the skirt is preferably inset an amount equal to the amount.

of the relief as indicated at 26 in Figure 1.

In operation the skirt flexes in several different ways and the various flexures blend or combine together to uniformly distribute thetotal flexing and the bearing pressures. Since each thrust face 15 and I6 is free from the head at-its upper edge neither face resists flexing of the other and either face may deform slightly to fit the contour of the engine cylinder, such flexing occurring along elements of the wall of the skirt. Because the wrist pin bosses are rigidly connected to the head they are separated or pulled apart in accordance with the diametrical expansion of the head parallel to the wrist pin axis. This separation of the wrist pin bosses pulls the skirt apart and increases the diameter A-A in Figure 5 while correspondingly decreasing the diameter BB. Because the diameter AA is but slightly shorter than the diameter BB, however, this movement .is insufficient to compensate for the excessexpansion of the piston through any given tempera- .along the lower edge of the slot 11 1 of one of the leaves the stifl'ness of thrust face it two substantially triangular seg- 5 ments 21 and 28 connected to the remainder of the skirt wall along the spiral lines joining the drilled hole 23 with the opposite ends of the horizontal slot 11. This produces a substantial resistance to the inward flexing of the leaves 21 and 1 28 varying with the amount which the leaves are pressed inwardly from their normal contour and with the width of the portion at the center of the thrust face I! engaging the cylinder wall. Such flexing of the leaves 21 and 28 combined with the 1 reduction in length of the major axis BB resulting from the separation of the wrist pin bosses compensates for the excess expansion at the upper end of the skirt.

As the piston is heated up and the skirt expands the separation of the wrist pin bosses, and consequent approach of the oval contour of the skirt toward a circular contour. moves outwardly toward the cylinder wall-the pivoting lines about which the leaves 21 and 28 bend as they are pressed inwardly from what would be the normal contour of the skirt at a particular temperature. As a consequence the flexing of the metal incident to inward bending of the leaves 21 and 2| is greatlyreducedand is distributed through a wide area of the skirt. An exaggerated illustration of the relation of the skirt to the cylinder wall at the upper end of the, skirt after the piston has been heated up is shown in the diagram,

Figure 6. It will be apparent that the minor axis is A-A as shown in Figure 5' has increased to the diameter A-- in Figure 6. It will also be ap-. parent that the leaves 21 and 28 have been bent inwardly through a substantial portion of their length from what would be their normal contour at that particular temperature and into full close engagement with the cylinder wall throughout the width of the portions which have been bent. It will be apparent by comparison of Figure 8 with Figure 5 that the amount which the metal has been bent to bring the leaves 21 and 28 into the relationship with the cylinder wall illustrated in Figure 6 is substantially less in-view of the increase in length of the minor axis to. the diameter A'-A' than would otherwise be required to bend the leaves to the positions illustrated in Figure 6. In other words considering the leaves 21 and 28 as springs the adjacent ends of the springs have been bent inwardly but the amount of bending in the springshas been reduced and has been more widely distributed by moving outwardly the remote or relatively fixed ends of the springs.

The unit bearing pressures are maintained uniform by the same combination of flexures. The

points of maximum flexibility resulting from the slotting are the points of the leaves 21 and 2| at the intersection of slots l1 and 22. Proceeding from the point the metal section increases as the point of support is approached. This increase in stiffness, however, does not result in higher and higher unit pressures, because the clearance increases as a result of the oval contour of the skirt of the "leaves 21 and 28 decreases as they are bent inwardly so that as more and more bearing width comes into contact with the cylinder wall as a result of flexing of the leaves 21 and 28 the flexlbility of different points and the flexibility 7'0 across the width of the 7's pressures effected by this invention.

portion bearing tends to remain similar. 'loo' rapid a decrease in the flexibility of the center ofthe thrust face is prevented by the simultaneous decrease in the degree of ovality of the thrust face as a result of the separation of the wrist pin. bosses and the consequent moving outwardly of the zones of bending of the leaves 21 and 28. The unit pressures are thereby maintained uniform throughout the width of the portion bearing at any time.

Considering the minimum thrust face vertically, it is apparent that starting at the corners of the leaves 21 and 28 and proceeding downwardly, the flexibility of the section due to the slotting decreases as the point of support represented by the lower end of the slot is approached. The decrease in flexibility is compensated for by an increase in the flexibility of the skirt as a whole as the open unsupported end of the skirt is approached. The unit bearing pressures are thereby maintained uniform vertically throughout the height of the'skirt. 7

It has been found that with this piston construction it is possible to flt the pistons to a relatively small clearance so as to eliminate all slap and minimize oil pumping when the piston is cold and to operate the engine at speed as high as 4500 to 5000 R. P. M. without danger of the piston scoring or binding in the cylinder because of the uniform distribution of the bearing At the same time the life of the pistons has been greatly increased-under high speeds and temperaturesbecause the uniform distribution of bearing pressures results in low unit pressures and consequent minimized surface wear and because the uniform distribution of the flexing which occurs during compensation for the excess expansion of the piston skirt eliminates the danger of fatigue failure at any point. At full operating temperae tures and at high speeds it is possible to obtain an almost complete circumferential bearing of the piston upon the cylinder wall without excessive pressure at any point.

While I have illustrated and described a preferred embodiment of this invention it is to be understood that many variations and modifications of structural details may be resorted to without departing from the scope of the invention as defined in the following claims.

I claim:

r 1. An internal combustion engine piston composed of a material having a co-efflcient of thermal expansion higher than cast iron comprising a head having a depending ring flange, wrist pin homes depending from and rigidlyconnected to said ring flange, and a relatively thin walled skirt integrally connected at its upper edge to said ring flange in the region of said bosses and separated at its upper edge from the ring flange on both sides of the bosses by two arcuate horizontal slots, one side of said skirt being formed with a substantially vertical slot intersecting one of said horizontal slots substantially at its center and extending toward but terminating short of the open end of the piston skirt leaving a circumferentially continuous cylinder bearing ring at the open end of the piston skirt below the end of said substantially vertical slot, and said skirt being oval in contour with its major axis perpendicular to the wrist pin axis.

2. A one-piece internal combustion engine piston composed of aluminum alloy comprising a head having an integral ring flange, and a skirt having aligned wrist pin bosses and opposed thrust faces, said skirt being integral with said ring flange above said bosses and separated therefrom above said thrust faces by spaced arcuate slots, one of said thrust faces bein formed with a substantially vertical slot intersectingone of said arcuate slots and extending toward, but stopping short of, the open end of the-skirt, leaving a circumferentially continuous ring at the open end'of the skirt, the other of said'thrust faces being circumferentially continuous and unslotted below the other of said arcuate slots, and said skirt, including said thrust faces, being ovalv in cross section with its major axis perpendicular to the axis of said wrist pin bosses.

3. A one-piece internal combustion engine piston composed of aluminum alloy including a head having a depending ring flange, a skirt having aligned wrist pin bosses formed therein and opposed thrust'faces laterally integral with said wrist pin bosses, said skirt being integrally connected at its upper edge with said ring flange in the region of said wrist pin bosses and separated therefrom by spaced arcuate horizontal slots above said'thrust faces, one of said thrust faces being formed with a substantially vertical slot intersecting one of said arcuate slots and extending towards, but stopping short of, the open end of said piston, the other of said thrust V faces being continuous and unslotted below the other of said arcuate slots, said skirt, including said thrust faces, being oval in cross sectional contour with its major axis perpendicular to thewristpin axis.

. x v v FRANK JARDINE. 

